docs: recommend Parquet and storage policies for compression instead of ZFS

[javier]

Summary

ZFS used to be the only way to compress QuestDB data, but it works outside the database. Parquet partitions are now the recommended approach: converted by hand on OSS, or automatically with storage policies on Enterprise.

• AWS, Azure, GCP: recommend ext4/xfs, compress with a TO PARQUET storage policy, and tier to object storage with TO REMOTE for further savings (cheaper storage, a single shared copy across instances, history beyond one volume)
• Enterprise quick start: fold compression and storage policies into one step, explaining that storage policies also compress data on local volumes, not only tier to cold storage. Removes the ZFS setup (which had a broken zpool command) and updates the compression FAQ
• Capacity planning: drop the claim that ZFS is required for compression
• ZFS compression page: add a warning recommending Parquet
• Remove the misleading Docker ZFS storage driver note and an unused file system snippet

[github-actions]

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